LONDON (10-Aug) -- Always unpredictable, the qualifying heats of the men's 1500m, and women's 800m and 5000m saw the elimination of reigning Olympic and world champions here tonight at London Stadium on the seventh day of the IAAF World Championships in Athletics.

In men's 1500m qualifying, the biggest casualty was 2016 Olympic champion, Matthew Centrowitz of the United States. Centrowitz, who has been plagued by medical problems this year including left and right abductor strains and a viral illness, was unable to sprint with the other 13 competitors in the final 120 meters of the first of three heats, finishing last in 3:48.34.

"It's kind of been a culmination of everything that's been going on this year, all the things I've been battling, and it's been really hard the last few weeks," a downcast Centrowitz told reporters. He continued: "Everyone goes through injuries. This year, just more than I've every had in one season. I just felt like I never really was able to get more than a couple of weeks good training and healthy training."

Both of Centrowitz's USA teammates, Robby Andrews and Johnny Gregorek, advanced. Andrews got the sixth and final automatic qualifying spot in the second heat in 3:43.03, while Gregorek advanced on time in the third heat, finishing seventh in 3:39.62.

All four Kenyans --Elijah Manangoi, Asbel Kiprop, Ronald Kwemoi and Timothy Cheruiyot-- advanced to tomorrow's semis-finals. Manangoi and Kiprop finished one-two in the slow first heat in 3:45.93 and 3:45.96, respectively, while Kwemoi advanced on time from the second heat in 3:43.10, and Cheruiyot finished second in the third and final heat in 3:38.41.

"Hopefully tomorrow I'll make it to the finals," said the always analytical Kiprop, the three-time world 1500m champion. He continued: "I cannot underrate anyone."

Nick Willis, the two-time Olympic medalist from New Zealand, also advanced sprinting confidently in the closing meters of the second heat to finish fifth in 3:42.75 and getting an auto qualifier. Willis, 34, started his season late this year so he could be sure to be fresh for these championships. He's only run three track races so far this season.

"There's less than 24 hours turnaround to the semi-finals, so all that mattered was getting through; I used as little as possible energy," Willis told reporters. "I felt a little sluggish, but not tired from working too hard... I got through fine."

WORLD CHAMPION OUT IN WOMEN'S 800M

The opening round of the women's 800m looked more like roller derby in some cases with athletes frequently bumping, throwing elbows, and even pushing their way through their fellow competitors.

"It's messy, bumper cars," lamented Canada's Melissa Bishop who finished second in the heat 2 to advance to the semi-finals, but nearly fell.

In the fourth of six heats, Marina Arzamasova of Belarus, the reigning world champion, was well-positioned to qualify as she ran down the homestretch near the lead, but her legs began to lock up and she was outkicked by Kenya's Margaret Wambui, Britain's Lynsey Sharp, and Uganda's Halima Nakaayi to finish fourth in 2:01.92. That time was too slow to advance as one of the six fastest losers, putting her out of the meet.

Also failing to advance was Iceland's Aníta Hinriksdóttir, the 2017 European Indoor Championships bronze medalist, who finished fourth in heat 4 in 2:03.45.

"I ran like shit," Hinriksdóttir told Race Results Weekly.

The key medal favorites all got through to the semi-finals, including the "Big Three" of Caster Semenya of South Africa (first, heat 3), Wambui (first, heat 4) and Francine Niyonsaba of Burundi (first, heat 6). Niyonsaba was the only woman to break two minutes, clocking 1:59.86.

"Everything is under control," replied Niyonsaba when a reporter asked her if she had run too aggressively. "It's under control. I have been training well, I'm in good shape. So, I expect to do more."

Brenda Martinez of the USA, the silver medalist in this discipline in the World Championships in Moscow in 2013, lost valuable energy trying to solidify her position because of excessive pushing and shoving (she actually helped Bishop to stay on her feet by reaching out with her arm), then had precious little left for the final sprint where she tied up and only finished fourth in 2:01.53. She had to wait for the next four heats to play out, and in the end she had the second to last time qualifier and advanced.

"I felt like for the majority of the race I was, I felt like in control," Martinez said. "But, everyone had a kick, so, I just wasn't aware of who was behind me." She continued: "I'm kind of pissed off with the way I finished."

Martinez's two USA teammates, Ajee' Wilson and Charlene Lipsey, both won their heats to advance without difficulty.

FAST TIMES IN WOMEN'S 5000M QUALIFYING

Very fast times were posted in the first round of the women's 5000m: nine women broke 15:00, and 20 broke 15:15.

Most of the fast times came in the talent-laden first heat where the two gold medal favorites, Kenya's Hellen Obiri and Ethiopia's Almaz Ayana, finished one-two in 14:56.70 and 14:57.06, respectively.

"I feel good, I prepared well and I want to do my best on Sunday now," Obiri told IAAF interviewers. "I am in very good form and I am not going to fear anyone. It will be a good race I am sure."

Despite running 14:59.34 in the first heat, Britain's Laura Muir had to advance on time. She tied up badly in the homestretch, looking fatigued.

All three Americans --Molly Huddle, Shelby Houlihan and Shannon Rowbury-- made it through to Sunday's final. Rowbury was a comfortable fifth in the first heat, clocking a season's best 14:57.55.

"For some reason, the heats were so unevenly distributed, at least on paper," Rowbury observed. "So, I knew heat 1 would be a tough one. I cut it close at the end, but I got the automatic and just focus on Sunday."

Molly Huddle ended up leading nearly the entire second heat, building up a big lead of perhaps 50 meters. But the former USA 5000m record-holder was run down by the field in the final lap and passed by six women in the homestretch, including her own teammate Houlihan and medal hopeful Sifan Hassan of the Netherlands. Huddle made it through on time in 15:03.60.

"I kind of knew 15-flat was the time, so I thought, I don't have very good closing now," Huddle told reporters. "I'd rather run 72's (15:00-flat pace). I'll see if anyone goes, but I ended up in the front." She continued: "It turned into a nightmare; I was just waiting for them to catch me."

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